In recent years, as the Internet has come explosively into wide use, cases of establishing LAN (Local Area Network) in offices and homes have increased. With the aid of progress in digital radio communication technology, and due to inconveniences of cable wiring, so called wireless LANs, which establish a LAN wirelessly are greatly required. Moreover, with the aid of the fact that the wireless LAN can be used in mobile environments by mobile terminals typified by portable computers, it is expected that wireless LANs will be used in large numbers in the future.
An example of the wireless LAN technology includes IEEE802.11 which is already standardized in IEEE(Institute of Electrical and Electronics Engineers). The standardized technology defines an OSI model, from a physical layer to a MAC (Media Access Control) layer which is a lower layer of a data link, can displace the Ethernet (registered trade mark) which is a wire LAN transmission line, and has further a specification which can also provide a roaming function which is an additional function by virtue of being wireless.
Moreover, domestic use of radio transmission apparatus has increased. There are more and more occasions in which even a video signal system, such as video and audio, is digitized and wirelessly transmitted from a fixed transmitter to a mobile receiver, for viewing and listening. Meanwhile, a limited frequency band available without license causes increase in mutual interference between radio apparatuses or between apparatuses which emit electromagnetic waves. Therefore, when manufacturing a radio apparatus, it is important how the interference caused by another radio apparatus or electromagnetic wave emitting apparatus is dealt with.
As an example of measures to be taken to deal with interference, an audio data communication device is disclosed in Patent Document 1.
(Patent Document 1)
Japanese Unexamined Patent Publication No. 7-283757/1995 (Tokukaihei 7-283757; published on Oct. 27, 1995). With this audio data communication device with which it is possible to minimize reception data loss rate due to data error, even when noise in the reception environment increases, by variable bit rate compression of audio.
FIG. 12 illustrates an arrangement of the audio data communication device disclosed in Patent Document 1.
In FIG. 12, an audio data transmission device 200 transmits audio data which an audio data reception device 201A receives. In the audio data reception device 201A, a CRC (Cyclic Redundancy Check) bit judgment device 201E detects an error in the received data. According to an error rate judged by an error rate judgment device 201F, retransmission instruction message generator 201G generates a message which specifies a data compression rate and a number of times of retransmission at a transmission end. The message is transmitted to the audio data transmission device 200. According to the message, a coder 213 compresses data to the specified data compression rate. A CRC bit generation device 214 adds a CRC bit to the compressed data so as to generate a compression data packet, and stores it in a data buffer. Meanwhile, a retransmission counter 216 counts the number of times specified by the message. The compression data packets are read out of the data buffer 215 by the counted number of times, aligned in one frame, and transmitted from a transmitter 219.
However, in such a conventional radio communication apparatus, it is supposed that a variable bit rate compression method is used. This requires changing, according to an error rate, the compression rate and the number of times of retransmission for each data packet transmission. Therefore, if the communication state deteriorates, it becomes difficult to maintain a constant data quality. This results in a lowered quality of the entire video-or audio to be transmitted.
The present invention is to solve the above mentioned problems and an object of the present invention is to provide a radio communication device with which it is possible to minimize deterioration of the video and audio data, even when the communication state deteriorates, and to transmit data without lowering the quality of the entire video and audio transmitted.